In recent years, in vehicle-mounted equipment, such as a car navigation device, a plurality of wireless communications methods are installed and used for various applications. For example, wireless communications using a Bluetooth method are performed between the vehicle-mounted equipment and a terminal, such as a mobile phone or an audio player, and are used for a handsfree call, a dial-up connection, music playback, etc.
Further, wireless communications using a wireless LAN method, such as IEEE802.11b/g/n, are performed between the vehicle-mounted equipment and a terminal, such as a smart phone or a tablet, and are used for various applications such as transmission of video image/music and navigation.
Wireless communications using a Bluetooth method and wireless communications using a wireless LAN method use the same 2.4 GHz frequency band. Therefore, there occurs a problem that when these wireless communications are used simultaneously, radio wave interference occurs, more specifically, the wireless communication methods interfere with each other and both the communication qualities degrade.
Further, wireless communications using a Bluetooth method, which are installed in, for example, a car navigation device have an automatic connection function of automatically establishing a communication connection with communication equipment with which pairing has been established.
At the time of making a request for this automatic connection, the car navigation device pages the Bluetooth device with which pairing has been established, such as a mobile phone. At this time, when receiving a response from the Bluetooth device which is the paging destination, the car navigation device makes an automatic connection. When not receiving a response from the device which is the paging destination, the car navigation device continuously or periodically makes an automatic connection request until the car navigation device can make a connection with the device.
According to the Bluetooth specification, it is necessary to, in the paging operation, use 32 frequency channels which are determined uniquely from the device address of the Bluetooth device which is the destination slave. Therefore, a channel to be used cannot be selected at the time of the paging operation, and the automatic frequency hopping (AFH) function does not work. As a result, the frequencies used for Bluetooth and those used for wireless LAN cannot be separated from each other, and radio frequency interference cannot be prevented from occurring. Similarly, according to the Bluetooth specification, time slots are continuously used in the wireless communications using the Bluetooth method at the time of the paging operation. Therefore, the wireless communications using the Bluetooth method and those using the wireless LAN method cannot be used in a time-sharing manner.
As a method of preventing such radio frequency interference as above due to a paging operation for Bluetooth, there can be provided a method of giving a higher priority to either a wireless LAN or Bluetooth.
For example, patent reference 1 discloses a device that controls the priority of a wireless LAN and that of Bluetooth in MAC levels, thereby preventing radio frequency interference in wireless communications using the wireless LAN and those using Bluetooth.
The device described in patent reference 1 gives a higher priority to Bluetooth packets at the time of performing a paging operation for Bluetooth to give a higher priority to Bluetooth than to the wireless LAN, thereby preventing radio frequency interference.